The present application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 2000-327553 filed on Oct. 26, 2000, the entire content of which is incorporated herein by reference.
The present invention is generally directed to an electromagnetic valve.
One of the conventional electromagnetic valves is disclosed in, for example, Japanese Patent-Laid Open Publication No. Hei. 10 (1998)-122412. This conventional electromagnetic valve is composed of a coil-mounted yoke, a sleeve fixed to the yoke and having plural ports, a plunger arranged so as to be slidable relative to the yoke, and a piston slidably fitted in the sleeve for opening and closing the respective ports. When the coils are energized, the resultant magnetic flux applied to the plunger causes the plunger to slide relative to the yoke, which results in sliding movement of the piston relative to the sleeve, thereby opening and closing the respective ports of the sleeve.
In this conventional or prior art electromagnetic valve, the plunger and the piston are slidably supported by the yoke and the sleeve, respectively, in independent mode. The plunger and the piston are arranged in face-to-face manner and the piston is urged by a spring toward the plunger in order to engage an end of the piston with an end of the plunger.
However, in the above structure, due to the fact that the plunger and the piston are slidably supported by the yoke and the sleeve, respectively, in independent mode, to establish the engagement between the ends of the respective plunger and piston, the plunger and the piston have to be supported by the respective yoke and sleeve in greater precision so that the relative position between the plunger and the piston is made adequate. In addition, for slidable supports of the plunger and the piston on the respective yoke and sleeve, journaling bosses have to be provided on the respective yoke and sleeve. This also results in higher production cost of the device and in increasing the number of parts which is a cause for disturbing the downsizing of the device in the axial direction.
Thus, a need exists to provide an electromagnetic valve which can be produced at a lower cost, in order to overcome the aforementioned drawbacks.
The present invention has been developed to satisfy the need noted above and the present invention provides an electromagnetic valve comprising:
a coil-mounted yoke;
a sleeve fixed to the yoke and having ports;
a plunger slidably arranged in the yoke; and
a piston slidably arranged in the sleeve and opening and closing the ports, respectively,
the piston and the plunger being integrated with each other in such manner that an outer surface of the plunger and an outer surface of the piston are made coplanar in an axial direction,
wherein the plunger is brought into sliding movement relative to the yoke resulting from an electromagnetic flux acting on the plunger when the coil is excited, which causes the piston to slide relative to the sleeve, thereby making the piston open and close the respective ports.
In accordance with the first aspect, the piston and the plunger are integrated with each other in such a manner that the outer surface of the plunger and the outer surface of the piston are made coplanar in the axial direction, which makes it possible to furnish the outer surfaces of the respective plunger and piston concurrently by machining, thereby establishing a coaxial arrangement between the piston and the plunger with ease. Thus, the relative position relation between the piston and the plunger is made precise easily, thereby making it possible to lower the production cost. In addition, the plunger or the piston can only be supported on the sleeve or the yoke in sliding mode, which makes it possible to reduce the number of journaling bosses when compared to the conventional or prior art electromagnetic valve. Therefore, attaining lowering production cost and downsizing device in the axial direction by reducing the number of parts are made possible.
Preferably, the yoke is desired to be in the form of an integrated structure of a front yoke portion, a rear yoke portion, and a non-magnetic portion interposed between the front and rear yoke portions, the yoke being formed therein with an inner surface which has two portions, one being fixed with the sleeve, the other being used for a path to the plunger through which the electromagnetic passes.
Preferably, it is recommended that the piston is formed with an axial portion which passes through the plunger, the plunger being fixedly mounted on an outer surface of the axial portion.